System of radio broadcast distribution



Jan. 5 1926.

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Jnwntoz Patented Jan. 5, 1926.

UNITED STATES PATENT OFFICE.

SYSTEM OF RADIO BROADCAST DISTRIBUTION.

Application filed July 14, 1924. Serial No. 726,021.

To all whom it may cancer-n:

Be it known that I, EDWARD E. CLEMENT,

a citizen of the United States, residing at Washington, in the District of Columbia, have invented certain new and useful Improvements in Systems of Radio Broadcast Distribution, of which the following is a a specification, reference being had therein to the accompanying drawings.

My invention relates to systems of communication, and particularly to telephone and radio systems. It has for its objects, among others, the following: To organize radio broadcasting service on a commercial basis, and to control the service units or receiving stations so that the various contingencies incidental to commercial operation may be efficiently met.

The foregoing objects are attained by the method of operation to be hereinafter described, which, it is to be understood, is typical, and is to be taken as such, for purposes of definition and not of limitation of 425 the invention. According to this method I provide a system having for its basis the distribution among regular subscribers in localized areas, of standardized receiving instruments, each local area taking its broadcasting service from its own central station on such wave length as may be fixed and determined for that area. Each receiving station is connected to the local central station by a wire circuit, through which both distribution and the control of the local station are attained.

With the above arrangement for distribution, by which the ultimate receiving instruments are reduced to the simplest form compatible with their purpose, I am enabled to concentrate apparatus requiring more ela' boration and careful adjustment at the local central stations. These are so related to existing high power broadcasting stations, and to others equipped as a part of the system, that uniform service and uniform programs may be distributed to the local central stations according to a regular schedule, and the cost of the primary broadcasting, as well as an special programs put on by the local distri uting stations, and the operation of the same will be borne by the subscribers by way of ultimate distribution in individual charges against them.

One method which I use and shall claim herein for effecting this local broadcast distribution of matter received from primary stations, is by use ofdouble modulation at the primary station or stations where the primary wave is very short, say of the order of 75 meters modulated by an intermediate or long carrier wave, say of the order of 500 meters which long wave is modulated with the audio signals to be transmitted. The short or primary wave is picked up by a secondary station at a local distributing center and the intermediate or long carrier wave detected out, amplified and radiated out over the local area for reception at the private local receiving stations. An advantage of this method is that the control, and responsibility of maintaining constant the carrier wave of the secondary or local distributing station or stations is delegated to the primary station, which of course requires less skill in the operation of the secondary stations and prevents interference in cases where a private receiving station may be located between or in the overlapping areas of two or more secondary distributing stations.

My invention is illustrated in the accompanying drawings, in which:

Fig. 1 is a diagram showing a general system embodying the same;

Fig. 2 is a diagram showing a central station telephone switchboard, subscribers lines terminating thereon, and subscribers telephones connected thereto;

Fig. 3 is a diagram to be read in connection with Fig. 2, showing the radiophone set at one of the subscribers stations, and the radio switchboard and associated equipment at the central station;

Fig. 4 is a diagram showing a substation battery charged and controlled over a phantom circuit imposed on a metallic magneto telephone circuit;

Figs. 5, 6, 7 and 8 are schematic circuits showing methods of connecting the radio battery with relation to the centralized telephone battery;

Fig. .9 is a diagram of a modified arrangement of circuits.

Fig. 10 is a diagram of the circuits of a primary station capable of broadcasting on double modulation.

Fig. 11 is a diagram of the circuits of a secondary or local distributin station capable of receiving the short, ouble modulated wave of Fig. 10 and redistributing the intermediate or long carrier wave.

Referring to Fig. 1, 1, 2 and 3 represent telephone subscribers stations connected by wires 4, 5 and 6 to the central telephone exchange 7, constituting the distributing center for the area in which local subscribers 1, 2, 3, etc., are located. Superposed upon this telephone system is a radio broadcast system comprising a central station 8 and subscribers station 1*, 2, 3", etc. The central radio station or exchange is provided with switchboards and a complete broadcasting equipment, and the subscribers stations 1, 2 3*, etc., are provided with receiving instruments all standardized for the same wave length, and adapted to respond to the waves radiated from the central station 8. The interrelation between the telephone system and the radio broadcast system is by means of physical connections indicated at 1", 2", and 3 at the subscribers stations, and multiples or trunk extensions 15 from the telephone exchange switchboards to the radio broadcast exchange switchboard in station No. 8. The detail of these connections will appear hereinafter, but it should be stated here that the system of connections is such that telephone wired traflic has the right of way over the Wires, while the radio traffic has the right of way over the radio side of the system. The arrangement is such that the radio operator cannot interfere with telephone operation, nor can a telephone operator interfere with the radio operation, although under proper conditions each can act freely by way of borrowing facilities from the other. At all times, should a question of precedence arise, the apparatus is arranged so as automatically to cut off the radio connections and to leave the wired lines clear for telephonic use. Stations 12, 13 and 14 in this figure are typical of indifferently located distant stations which may or may not be a part of this particular system. As the figure is typical only, no attempt has been made to give the geographical location of such stations or to show the actual arrangement and distribution of the tele Jhone centers through which final broadcastlng to the subscribers must take place. The main purpose of this figure is to crystallize the method employed, by which the development of a very large number of unrelated individual receiving stations is replaced by an orderly system of distribution through the telephone centers, whereby the individual receiving instruments are localized, maintained, controlled, and supplied with definite service through regular channels, for which a definite charge can be made and collected in the manner usual 1n wired systems of communication.

Inasmuch as the number of wave lengths available for transmission is limited in the present state of the art, advantage is taken of the organized system of wire distribution and localization to create a phantom system controlled and guided thereby.

Briefly stated, as indicated in Fig. 1, each radio central station or radio department of a telephone exchange, is not only provided with broadcasting equipment for its subscribers, but also with radio receivers adjustable by tuning to wave lengths allotted to such stations as those indicated at 12, 13 and 14, as well as primary stations maintained and operated by or under the direction of the telephone organization itself. By means understood in the art, messages received at the radio central stations are relayed on their respective standard wave lengths to the local subscribers.

Referring to Figs. 2 and 3, I have therein shown circuits of the central office and substation equipments and connections, Fig. 2 representing the telephone side of the system, and Fig. 3 the radio broadcast side of the system. Before proceeding to detail description it may be noted that in accordance with standard telephone practice, provision is made for keeping the telephone lines and central office circuits clear of all grounds or other disturbing connections during conversation. lVhen the radio broadcast apparatus goes into service, by closing the filament switch its operation in receiving is identical with that of any radio receiver, and in the event that use is made of any partial transmission of waves over the line wires, as will be hereinafer pointed out, said waves will be at a frequency above or below the limits of audition. In the present diagram, Figs. 2 to 9 inclusive, I have shown the circuits arranged with nothing but continuous current for radio purposes over the telephone line Wires. This is the simplest form of control and the one nearest to present-day telephone practice, and is absolutely certain not to produce any disturbance in adjacent conductors in the telephone cables. Each radio broadcast set is provided with a cut off relay energized when the telephone set goes into commission, either by calling or being called, and at the central office whenever the radio operator takes control of the line, he disables it in the usual manner by pulling up the cut oil relay at the telephone switchboard, thi however being subject to the condition that a special tone test may be put on, so that all operators may know that the line is held on the radio board, and subject to interruption for telephone connect on. I prefer to use this tone test only with the radio operators testing plug. because his regular connecting plug includes within its functions that of connecting a subscriber through the station amplifier to th b casting transmitting set, and a connection of this character should not be interrupted without permission.

Referring now to the diagrams, Fig. 2. A and A are two subscribers stations connected by line wires 1(i17 and 18-19 respectively to the central station C where they terminate on jacks J and J. PP are plugs forming the terminals of a cord circuit 20-21, 2223, having a bridged repeating coil I, ringing and listening keys K and K, supervisory signals ss and bridging connection to the main battery B. The same battery is shown supplying current to the line relays L, L, and through contacts at the cut off relays L L to the respective lines for calling purposes. In this system, when a subscriber takes down his receiver, the line relay lights its lamp, which is extinguished when the operator inserts the answering plug. Battery supply for the connected lines is thereafter taken through the cord circuit 2022, 21-23, in a manner well understood in the art. \Vhen the substation telephones are out of service, with their receivers hanging on their hooks, the line circuits are conductively open for direct current, leaving the ringers Q and Q, in circuit for alternating ringing current passing through the condensers q-g.

Referring now to Fig. 3, it will be observed that the radio switchboard which I have designated generally by the letter R, is connected to the subscribers lines by multiple taps marked 16, 17, and 17 and 18 19 19". These terminate on multiple jacks J J corresponding to the multiple jacks on the telephone switchboard. It should be noted that throughout this system the tip wire 16 and 18 with their branches are connected to ground. while the sleeve wires 17 and 19 and their branches, are connected to battery. This is extended into the radio side of the system for the purpose of securing proper balance between the main battery or power plant of that side and the main battery or power plant of the telephone side of the system.

At the subscribers stations taps are also taken oil from the telephone terminals to the broadcast receiver terminals as indicated at 18", 19 and 19 (The broadcast receiver is shown only at one substation for sake of simplicity of illustration). The two branches 19 and 19 are taken from the sleeve or battery side of the l ne 19. and are connected to opposite terminals of the winding of a relay L*. which constitutes the substation cut off relay for the broadcast receiver. The winding of this relay is bridged by a condenser 9' through which both ringing and voice currents can pass without substantial impedance. lVhere the broadcast receiver is attached to a party line substation, this relay L may be omitted, since on such party lines there are usually grounds on one side or the other. As will presently appear, the radio circuits described herein are applicable to two-party or four-party lines, with individual metering of the party stations.

Normally, that is to say when the telephone circuit is not in use, the cut oif relay L is deenergized and as a consequence the wire 19 is connected through a back contact of the relay through extenson wire 24 to the branch 25 connected to the A battery marked A in Fig. 3. The wire 18 similarly passes through a back contact of the relay to the extension wire 26 leading to test or listening relay 27 and ground. 18", it will be remembered, leads to the tip or ground side of the line, therefore it is the side which in the radio broadcast system canbe made use of with a permanent ground or grounds, without disturbing the balance of the telephone circuit.

The radio broadcast receiver at the substation A is shown as comprising an antenna 28, tuned coupler 29, detector tube 30, audio amplified tubes 31 and 32, and the usual transformers 33, 34-, 35, the last mentioned transmitting the amplified audio waves to the telephone receiver or loud speaker 36. The filament battery is A,. The plate battery is B and suitable tuning condensers and coils, tickler coil for regenerative efl'ects, etc., are provided as required. I should remark in passing that this representation of the radio receiver is intended to be typical only. The present invention does not concern itself specifically with the design of the local radio-broadcast sets, and other circuits and apparatus may be substituted for those shown in the diagrams without departure from the invention.

The relay L has four pairs of contacts, one pair 27 closing the wires 25 and 37 from battery A, to the filaments. The second pair 27 closes the wires 25 and 38 so as to put battery A on the radio broadcast transmitter T, and through the induction coil I, to ground. The third and fourth pairs of contacts 27, 27, close the wires 39 and 40, forming terminals of the secondary induction coil circuit I. to the tip and sleeve side of the telephone line respectively, through the back contacts of relay L. The transmitter T is shown hanging upon a hook switch 11 controlling the connection of wires 41 and -12, constituting a parallel link between the battery A, and the filament bus -13. Thus the filament can be heated and the broadcast receiver put in service either through the agency of the relay L or by the switch hook H. The former is controlled by the radio operator at central, and the latter by the subscriber at the substation. In addition to the hook, the subscriber has a manual switch 71. by which he can connect the battery wire 42 through a III wire ii to his transmitter T, coil and ground, so as to energize his talking circuit. I provide an ordinary telephone receiver t in series with the secondary of the induction coil I, and I interpose a pair of condensers Q3, (1 between the secondary of the induction coil 1, and the receiver t on the one hand, and the terminals of relay L on the other, so that while the subscriber by means of switch 71 can connect his phone T't for receiving calls over the telephone line, he cannot originate calls thereover from the broadcast receiver extension.

Returning now to the central station, and particularly to the radio department thereoi shown in Fig. 3, T represents a broadcasting transmitter, symbolized in very simple form, but supposed to contain the usual elements of power supply, modulator, oscillator and aerial, with suitable a1nplification of the audio waves supplied on the input side. The jack J connected to the amplifier t and thence to the transmitter T, symbolizes a group of such jacks or equivalent. connecting means such as automatic switches, controlled by dials or keys for connecting any of the wire lines to said radio transmitter. Detailed appliances, both for the switching and for the radio transmission, are well known in the art, and need no specific description in this specification, my present invention having to do particularly with the method of transmitting by wave radiation to the substations, and of bringing in all conversation originating or received at the substation radio broadcast apparatus over the subscribers wire line. This includes repetition of modulated radio waves received at the radio broadcast substation and also originating messages gathered up and to be put through the amplifier t on the transmitter T for broadcasting.

It may be explained here that the transmitter, T for general purposes is assumed to be the standard wave length transmitter for the local exchange area, to which all of the substations are tuned and upon which they depend both for original messages and programs and for those received and relayed from a distance. There are special cases. however, in which certain groups of radio broadcast subscribers may desire intercommunication among themselves, and I contemplate therefore the installation of duplicates of this transmitter, which may be connected up for such group use. For example, a chess club desiring to meet, arranges a program, and at the appointed time its members attend at their broadcast receivers, all removing their transmitters T from their hooks, while the radio operator at the central station plugs up the multiples of their respective lines through their jacks J -J and connects them on to a special broadcasting transmitter of the type T. This plugging up may be carried out in any desired manner, there being several ways well known in the art for thus connecting telephone lines to ether. The radio operator then supervises the operation, since any one of the connected subscribers may be speaking through the broadcasting transmitter to the others, and it is necessary to prevent interruption. The same might be said of any meeting of a group of people held in this manner, the most valuable feature of this part of the invention being the absolute control afforded over the transmitted messages. The connection to the broadcasting transmitter is solely within the control of the radio 0 erator at the jack J or any other suitable orm of switch, and he has it in his power therefore to cut off connection at any time.

The cord circuit between plugs P and P in Fig. 3 is the same as the operators cord circuit in Fig. 2, but the radio operator also has special test cords such as that shown in the upper part of the figure connected to plug P. Here the keys KK' are of standard construction, as in the other cords, and the test contact of the plug P is connected through suitable resistance to the supervisory lamp 8 to the radio battery 13, means such as the commutator 10 being provided to give special tone test on the test thimbles of the multiple jacks J, J, J etc. It will be observed that the constant connection of the sleeve or battery wire 24 at the radio broadcast substation to the bus wire 25 of the battery A produces charging of that battery by the constant flow of current therethrough from the main radio battery B at the central oitice. The amount of energy thus delivered to the battery A, depends upon the size of the line wires, and the length of time available for such charging. As shown, the battery wire 24 is not cut off except when the cut off relay L pulls up which is only when the line wire is in use for conversation. With No. 19 line wires, and using only the sleeve wire for conduction, it would be possible to safely transmit from one-half ampere to two or three amperes, according to the line resistance and the voltage of the battery employed. \Vhere this voltage is standard manual telephone voltage, say 22, and the single wire resistance to the substation is from 25 to 50 ohms, it would be possible to maintain the battery A continuously charged, provided the time of discharge be not too long extended, and the charging be not interrupted by other contingencies, such as the excessive telephone use of the line. In Fig. 4 of the drawing I show means for charging such a battery over a phantom circuit composed of the two sides of a magneto telephone line. Such a phantom circuit of course possesses still lower resistance than a single wire of the pair and correspondingly augments the amount of energy that may be delivered without a prohibitive loss. I wish to point out in connection with this, that radio instruments have recently been devised by the commercial radio corporations, and also by the United States Bureau of Standards, which employ rectified alternating current for lighting the filaments of the audion tubes, such currents being stepped down to the usual voltage of the filaments from the voltage of house mains or feeder lines. Using such a type of transformer and rec-tifier circuit, it is within the scope of my invention, to feed the filaments direct, and at the same time charge a floating storage battery A, if desired, by transmitting over my line wire 19-19--24 a sine wave current at such voltage as will deliver the necessary energy.

Connected to the key K is a wire 50 containing a supplemental key is to connect the voltmeter or other suitable indicating instrument V and ground. The key K serves to connect the operators listening set, and also to put battery on the tip of the plug, by which means current is thrown out on the tip side 18 of the line, then through extension 18 and back contact of relay L to the winding of relay L and ground. The operation of these test keys will be obvious from the description. Key k enables the operator to take a reading on the battery A the line resistance being known, and the main batteries B, B being disconnected botl: at the cut off relays L L" from the line itself and by the back contacts of key K from the plug This is the most important test because the lamp filaments can be observed by the subscriber, and any defect therein reported over the telephone. A companion test however enables the operator to determine whether the radio-broadcast instrument as a whole is functioning properly, assuming the transmitter T to be hung upon its hook H, and as shown to have its mouth piece turned toward the emission orifice or diaphragm of the radio telephone receiver. Connection of battery set B to the relay L causes the subscribers telephone set T, I, to be connected to line and so to the multiple jack J plug P and the operators headphone connected through the. listening key K. It is assumed of course that some form of broadcasting is going 011 from the transmitter T, so that the radio operator not only gets a teston the performance of the individual subscribers broadcast receiver, but also gets a test on his own broadcasting transmitter and on the relative tuning of the same with respect to the subscribers station.

It should be noted that battery B in Fig. 3 is connected to the sleeve wires 17*, 19 through the contacts of cut off relays L", L", energized in parallel with the line cut oil relays L and L either from the radio board or from the telephone switchboard. This enables the central oflice under all cir cumstances to keep a talking line balanced and supplied with current only through the connective cord or switch circuit, but as shown in Figs. 5 to 8 inclusive, the connections of the radio battery and that of the main battery are such that the balance is normally maintained, and current is supplied in such a way to the sleeve side of the line that no signaling apparatus on the telephone switchboard is affected thereby.

Fig. 5 shows the condition when a subscriber is talking through the telephone switchboard, the repeating coil I and the main batter B being shown as bridged across the hue, and the radio battery B permanently connected through the sleeve side to the subscribers battery A Battery supply for both the subscribers transmitter and the battery A would as a matter of fact be drawn in due proportion from each of the centralized batteries B, B, and the resultant effect would be to divide the load between the two parallel sources, without changing the normal condition.

Fig. 6 shows the same arrangement when the subscribers telephone station is idle, and the main battery B is bridged across the line wires between the two windings 11 of the subscribers line relay on the telephone switchboard; while the radio battery is connected in parallel to the sleeve side of the line through low resistance choke coils ww' which do not appreciably reduce the potential placed upon the line terminal of the winding 1 of the line relay, which being exposed to balanced potentials, will not be energized unless the subscriber calls.

Figs. 7 and 8 show corresponding conditions with the out 01f relay L at the subscribers station for detachin the battery A, when the subscriber is talking.

It is not considered necessary to actually adopt a permanent connection of the radio battery B because telephone conversations are usually brief and the time of use of the current fiow in the sleeve wire would not be thereby greatly curtailed. At the same time I have provided means in the cut of? relays L, L to disconnect the battery B when the lines are plugged up for conversation as at at in Figs. 5 and 7, and when such cut off relays are employed, the choke coils w-ac' may be omitted, so that a practically perfect balance may be had across the terminals of the line relay 1. In other words, by using the cut off relays L", L", of Fig. 3, I am able to dispense with choke coils 00-02 and connect the battery or charging generator of any type as shown in Fig. 3.

Fig. 9 shows a modified circuit in which the telephone switchboard and iadio switchboard are provided with multiple line connections as before, the radio switchboard having connections to the radio broadcasting transmitter T and the radio operator having a full equipment of cords and plugs of known types symbolized at P". The substation is provided with a radio detector set and receiver 36, normally connected to the radio detector set through back contacts of the relay L which when energized by means of the operators key law at the radio board, will disconnect the receiver 36 and connect the radio detector set on its audio side directly to wires 5253 and so through the contacts of cut oil relay L to the line wires 16-17. As there is no battery shown for the detector set (which is typical only,) the radiocentral battery feed is omitted in this figure, which represents a very simple standardized system in which however the radio operator still has perfect control for all purposes of the substation radiophone. It should be noted that the continued energization of relay L disables the radio set, and by winding this relay so as to consume little current, this affords means to disconnect the subscribers circuit from the radio switchboard until an inspector can make his rounds and the instrument can be removed.

In Fig. 10 is shown the circuits of a primary station for carrying out the method of regional distribution by double modulation at a primary station and segregation and redistribution at the secondary stations, the circuits of the secondary stations being shown in Fig. 11. The transmitting system of Fig. 10 consists of a transmitting antenna 51 excited by a radio or high frequency oscillator D, the output of which is modulated by the modulator C according to the well known Heising method, with an intermediate or long wave produced by a long wave oscillator B coupled to the oscillator C by the inductance coupling 52, the oscillations of the oscillator Ii being in turn modulated with audio signals from the transmitter 53 through the modulator A. This system for transmission at double modulation is the same as that illustrated and described in the publication Principles of Radio Communication Morecroft, John \Viley & Sons, London, 1921, pp. 681-682. In the operation of the transmitter shown in Fig. 10 audio signals originating at the telephone transmitter 53 act through the modulator A to modulate the oscillations of the long wave oscillator B which oscillations are modulated through the modulator C on to the short or primary carrier wave produced by the oscillator D and radiated from the antenna 51.

In Fig. 11 is shown the receiving and retransmitting system of a secondary or regional distributing station such as the station 8 of Fig. 1 for receiving the primary waves transmitted by the transmitting station of Fig. 1, above described, detecting out and radiating the intermediate or long carrier wave to the subscribers station. This system of reception and regional distribution consists of a suitable receiving antenna 54 operatively connected, as shown, to the input circuit 56 of a detector which input circuit is tuned to the primary wave generated by the oscillator D of Fig. 1. Its output circuit 57 is coupled to the first of a series of amplifiers 58 and 59 through an input circuit 60 tuned to the intermediate or long carrier wave generated by the oscillator B of Fig. 1. The amplifiers 58 and 59 are coupled as usual through a suitable inductive coupling 61 the plate, of the last amplifier 59 being coupled through the inductance 62 and 63 to a transmitting antenna 64 having suitable capacity 65 included in its connection to ground 66 and so adjusted in relation to the constants of the inductance ,63 and antenna 64 to tune the antenna ground circuit to the intermediate or lon carrier wave to be transmitted. Inductive y coupled to the antenna 64 by means of the inductance 67 is a local modulator and oscillator 68 tuned to generate oscillations of the same wave length as that of the intermediate or long carrier wave of the double modulated wave, the modulator and oscillator 68 being provided with a microphone 69 of any known or other suitable form operatively associated therewith for the purpose of enabling broadcasting to be practiced at the secondary station.

In operation, the short or primary carrier wave sent out by the transmitting station of Fig. 10 is received on the antenna 54 and tuned coupling and input circuit 56 from which it is detected or demodulated by the detector 55 to take out the intermediate or long carrier wave which is amplified through the amplifiers 58 and 59 connected in cascade, and radiated out from the transmitting antenna 64 to the local subscribers. It is to be understood that any of the primary stations such as 12, 13, 14 of Fig. 1 may be equipped with the double modula-. tion transmitting circuit of Fig. 10 while the secondary distributing station 8 of Fig. 1, or several others like it within receiving radius of the primary stations may be equipped with the receiving and retransmitting circuit of Fig. 11.

If it be desired to have no grounds on the radio battery busses at substations, such as that on the A battery at station A, in Fig. 3, the ground wires may be carried through contacts on switch hook H, opened when the hooks are up. Many other details of operation may be introduced and changes made, without departing from the scope of my invention.

I claim:

1. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplying high fre quency carrier waves of different fr quencies, means at each station to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a signal, the frequency of the intermediate carrier being the same for each primary station, a secondary station having receiving means tunable to the different primary freuencies, means at the secondary station to emodulate the received doubly modulated carrier wave so as to produce the modulated intermediate frequency wave, and means atthe station to retransmit the modulated intermediate frequency.

2. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplying high frequency carrier waves of different frequencies, means at each station to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a signal, the frequency of the intermediate carrier being the same for each primary station, a secondary station having receiving means tunable to the different primary freuencies, means at the secondary station to emodulate the received doubly modulated carrier wave to produce the modulated intermediate frequency wave, means at the station to retransmit the modulated intermediate frequency to a plurality of subscribers receiving stations, the subscribers receiving means being tuned to the intermediate frequency.

3. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplymg high frequency carrier waves of different frequencies, means at each statlon to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a signal, the frequency of the intermediate carrier being the same for each primary station, a secondary station having receiving means tunable to the different primary freuencies, means at the secondary station to emodulate the received doubly modulated carrier wave to produce the modulated intermediate frequency wave, means at the station to retransmit the modulated intermediate frequency to a plurality of subscribers receiving stations, the subscribers receiving means being permanently tuned to the intermediate frequency.

4. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplying high frequency carrier waves of different frequencies, means at each station to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a signal, the frequency of the intermediate carrier bein the same for each primary station, secon ary stations having receiving means tunable to the different primary freuencies, means at each secondary station to demodulate the received doubly modulated carrier wave to produce the modulated intermediate frequency wave, means at each secondary station to retransmit the modulated intermediate frequency, and a plurality of subscribers receiving stations grouped about each secondary station in its local area, the receiving means at the subscribers stations being permanently tuned to the common intermediate frequency.

5. A radio system of intercommunication having a plurality of standardized uniform receiving stations divided into groups, all said stations being tuned to a common frequency and of scnsitiveness limited to the areas covered by their respective groups, a local transmit-ting station for each group operating at said common frequency, aplurality of primary high power stations transmittlng at different frequencies and means at each local transmitting station for receiving the different frequencies and transforming them to the frequency common to the standardized receiving stations for transmission thereto, while preserving the original signal modulations in carrier form.

6. A radio system of intercommunication having a plurality of standardized uniform receiving stations arranged in groups all said stations being tuned to a common frequency and of sensitiveness limited to the areas covered by their respective groups, a local transmitting station for each group operating at said common frequency, a plurality of primary high power stations transmitting at different frequencies, means at the local station to transmit an original message at said common frequency and means also at the local station to receive messages from the primary stations at different frequencies and to relay them to the receiving stations at their common frequency, while preserving the original signal modulations in carrier form.

7. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplying high frequency carrier waves of different frequencies, means at each station to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a low frequency signal current, a secondary station having receiving means tunable to the different primary frequencies, means at the secondary station to demodulate the received doubly modulated carrier wave so as to produce the modulated intermediate frequency wave, means to amplify the intermediate frequency wave and to transmit the same to a plurality of subscribers stations, means at each subscribers station to demodulate the received intermediate frequency wave so as toproduce the low frequency signal current, and means to transmit the low frequency signal current back to the secondary station.

8. A broadcasting system comprising a plurality of primary stations, means at the primary stations for supplying high frequency carrier waves of different frequencies, means at each station to modulate its carrier by an intermediate frequency carrier itself modulated in accordance with a low frequency signal current, the frequency of the intermediate carrier being the same for all the primary stations, secondary stations having receiving means tunable to the different primary frequencies, means at the secondary stations to demodulate the received doubly modulated carrier wave so as to produce the modulated intermediate frequency waves, means to amplify the intermediate frequency wave and to retransmit the same to a plurality of subscribers stations, means at each subscribers station to demodulate the received intermediatefrequency wave so as to produce the low frequency signal current, and means to transmit the low frequency signal current back to its secondary station.

9. A broadcasting system comprising primary high power stations using different wave lengths, secondary stations having receiving radio sets tunable to the different primary wave lengths, and also having relay transmitting apparatus controlled by the receiving sets and operating on a standard fixed wave length the same for all-secondary transmitters, means to transmit from the primary stations a carrier having a relatively short wave length doubly modulated in accordance with a signal and an intermediate carrier of the standard fixed wave length, means at the secondary stations to derive the intermediate carrier from the received doubly modulated carrier and thereby to operate the relay transmitting apparatus, subscribers receiving radio stations grouped around each secondary transmitting station in its local area and tuned to the fixed transmitting wave length thereof.

10. A broadcasting system comprising a primary station, a secondary distributing station and a plurality of local receiving stations related to the secondary station and all in permanent tune therewith, means at the primary station to transmit a high frequency carrier wave modulated in accordance with an intermediate frequency which is itself modulated in accordance with a signal, means at the secondary station to demodulate the received high frequency wave to produce the modulated intermediate frequency carrier, means at the secondary station to relay and redistribute the demodulated wave in its own area at the intermediate frequency, which is the frequency to which the local receiving stations are tuned, and means also at the secondary station to determine when its transmitter is actually tuned to the fixed wave length of its receiving stations.

' 11. In a radio telephone system, a transmitting station, a receiving station, means for supplying to said transmitting station a doubly modulated high frequency carrier wave, means at the local station to detect the high frequency wave to produce a modu-' lated intermediate frequency carrier wave, means to radiate said modulated intermediate frequency wave, a receiving set at the receiving station tuned to receive the intermediate frequency wave, and a wire circuit connecting the two stations with means to connect it to the receiving set at the receiving station and means to transmit over said wire, to the transmitting station, modulated current corresponding to the said modulated waves.

12. A broadcast distributing syste'n prising a primary high power transmitting station provided with a source of carrier waves having a short wave length, means to modulate said short wave carrier in accordance with a long wave carrier which is itself modulated in accordance with an audio signal wave, a secondary distributing station arranged to receive said primary carrier waves, means at the secondary station to demodulate the received wave to produce the long wave modulated carrier, means to amplify and to reradiate the demodulated wave, a plurality of subscribers stations grouped in a local area about said secondary station, and means at each subseribers station to receive and detect the amplified wave in said local area.

13. A broadcast distributing system comprising a primary transmitting station arranged to transmit a relatively long audio modulated carrier wave on a relatively short primary carrier wave, and a secondary distributing station arranged to receive said primary carrier wave, detect and amplify the said relatively long carrier wave and reradiate the same, together with subscribers stations grouped in a local area about said secondary station and equipped with means to receive and detect said amplified wave in said local area.

In testimony whereof I hereunto aflix my signature.

EDWARD E. CLEMENT. 

